Media processing devices, such as laser printers and media sorters, among others, may operate on various types of media, such as various papers or plastics. Printable papers might include wood-and cotton-based materials of different qualities, of virgin and/or recycled content, formed in different thicknesses, and with different surface treatments. Printable plastics may include similar variations, in both transparent and opaque forms.
For any given printer, the quality of text and images printed on various media may be dependent on a number of factors, not the least of which is media type. By adjusting the print process based on media type, print quality may be improved. For laser printers, in particular, it may be advantageous to adjust fusing speed based on the type of media, often expressed in terms of media weight. One method of identifying media weight involves measuring the thickness of the media, thickness generally being indicative of media weight. Typically, this is done using an inductive or eddy current sensor that touches the media as it passes through the printer. The sensor and its circuitry produce a signal that varies as a function of the distance between the sensor and a metal plate that underlies the media. Capacitive sensors have been proposed to measure thickness as well.
However, thickness may not be the best measure of media type or media weight due to the different types of materials that may be employed in producing media. Furthermore, thickness sensors typically are fragile and expensive, and may be subject to wear, as they often are in contact with the media as it is fed by, to, or within a media processing device.
The present invention involves identifying media type in a media processing device. A system according to one embodiment of the invention includes a thermal energy source and a thermal energy sensor. The thermal energy source and thermal energy sensor are arranged along a media feed path so as to accommodate transfer of thermal energy to the media by the thermal energy source, diffusion of such thermal energy, and subsequent sensing of such diffused thermal energy to determine a heat capacity of the media, such heat capacity being indicative of media type.